Site-specific recombination by the integrase MJ1 on mammalian cell

Integrase MJl from the bacteriophage ΦFC1 carries out recombination between two DNA sequences (the phage attachment site, attP and the bacterial attachment site, attB) in NIH3T3 mouse cells. In this study, the integration vector containing attP, attB and the integrase gene MJ, was constructed. The integration mediated by integrase MJ1 in Escherichia coli led to excision of LacZ. Therefore, the frequency of integration was measured by the counting of the white colony, which is detectable on X-Gal plates. The extrachromosomal integration in NIH3T3 mouse cells was monitored by the expression of the green fluorescent protein (GFP) as a reporter. To demonstrate integration mediated integrase MJ1 in NIH3T3 cells, vectors containing attP and attB were co-transfected into NIH3T3 cells. The integration was confirmed by fluorescent microscopy. The expression of GFP was induced in NIH3T3 cells expressing MJ1 without accessory factors. By contrast, the excision mediated by the MJ1 between attR and attL had no effect on the expression of GFP. These results suggest that integrase MJ1 may enable a variety of genomic modifications for research and therapeutic purposes in higher living cells.